What it is
How it works
Tech Docs (UCO only)
First Light 4/12/2014 !
People and project
Mounting on the Telescope
Instrument on Telescope
PSF Open/Closed Loop
Talk on AO at OSA
Table 1. Infrared throughput, emission background, and point source sensitivity.
See the Predicted Perfomance Limits Calculations by Sri Srinath for more details.
Table 2. Options available in the aperture and filter wheels of the ShaneAO science camera.
The system uses a guide star to probe the atmospheric turbulence at millisecond time scales and corrects for the distorted wavefronts using deformable mirrors. ShaneAO can be used in natural guidestar mode, where a bright natural star is used as the guide star beacon, or laser guidestar mode, in which an artificial guide star beacon is formed in the mesospheric sodium layer using a laser tuned to Sodium’s D2 line. In laser guidestar mode, the system still needs a reference tip/tilt star since the laser’s exact direction is randomized on its upgoing path.
The science camera uses a detector array that samples the field of view at better than Nyquist criterion for diffraction limited PSFs in astronomical J, H, and K bands. The detector is located within a cryogenic dewar that contains a cold pupil stop to baffle out stray light emission. It also contains one aperture wheel and two filter wheels. The aperture wheel contains slits, an occulting finger, and a pinhole. The filter wheels contain a selection of bandpass filters, grisms and a polarization analyzer (Wollaston prism). The filters and apertures available in the dewar are listed in Table 2 Other filters are available (2.2/0.04, H Cont., KCont. ND2).
Figure 2 shows the path of the light though the AO system and into the science detector.
Figure 2. Layout of the optical bench, shown with support structure removed for visibility (left). The optical path with key elements of the AO system labeled is shown on the right.
Adaptive optics has application to astronomy science programs where measurements and imaging details would otherwise be corrupted by atmospheric seeing blur. Examples of successful AO programs are:
AO is typically not suitable for wide field (>1/2 arcminute) work or large surveys (although a cadence of ~50 objects observed per night is feasible).
AO is not very accurate for aperture photometry in crowded field conditions.
Distinctions to be made between ShaneAO and the older Lick AO system are that the new system has:
An observer must plan carefully to be sure the system will be able to achieve the measurements desired. Software and staff assistance is available for exposure time calculations and signal-to-noise estimation that will depend on science wavelength, seeing conditions, brightness of target, point like or extended object, etc. In addition to the science targets, the observer may choose to observe reference stars for color, magnitude, and PSF calibrations.
General guidelines for planning:
The AO system and laser are generally operated by an AO specialist and a laser operator respectively. The observer controls the science camera through a graphical user interface . The interface provides setup of exposure times, readout modes, filters, etc. and gives a quick-look visual display of exposures. All operations are automatically logged with time-stamps. Setup information is extensively logged in FITS headers of the science data files. Information about the AO system operating parameters, measured seeing conditions and laser power are also entered in the logs and FITS headers.
Project ReportsYearly Project Reports to the NSF: 2010 2011 2012 2013
Design Review Presentation (April, 2012)